IT WOULD BE ANY FAMILY’S nightmare: the murder of a teenager, shot on the streets of Boston.

For Monalisa Smith, the death of her 18-year-old nephew in 2010 was a wound that will never heal, and an urgent call to action. She formed a group called Mothers for Justice and Equality - a grass-roots peace movement that has rallied the community. Smith’s team of like-minded mothers, convening at a church in Dorchester, dedicated themselves to preventing other families from suffering such devastating losses.

“For too long, violence has left mothers fearful and without a voice,’’ said Smith, 49. “We are empowering them to make change in their homes and neighborhoods.’’

With a $30,000 grant from The Boston Foundation’s StreetSafe Program, Smith, a Citizens Bank executive, prompted important urban change, including the passage of an ordinance to restrict the sale of street knives to minors; parent-to-parent mentoring; and empowerment breakfasts with legislative leaders such as Governor Deval Patrick.

More than 500 members now gather at the group’s “kitchen table’’ - a new office space in Roxbury, where neighborhood mothers are learning to be civic leaders.

The effort is visible. Smith’s group is placing dozens of billboards across Boston in an awareness campaign. They sport pictures of young victims, the human losses behind the group’s simple motto: “It’s not OK.’’

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